More than 200 cows would have been needed to produce the vellum sheets for the three hefty volumes of the manuscript, which contains 107 finely painted illustrations.
It was written in Flanders or Artois some time between 1315 and 1323 and probably produced for Guy VII, Baron de Rochefoucauld, head of one of the leading aristocratic families of medieval France.
The manuscript went on to be acquired by 19th century collector Sir Thomas Phillipps and has changed hands twice since.
The stories of Arthur, the lady in the lake and Lancelot which it contained were popular in their day and were translated widely around Europe, and became something of a guidebook for chivalry.
And the sale of the manuscript coincides with the third series of Merlin, which is shown on the BBC on Saturday nights.